It is common for heat pipe heat exchangers that utilize water as the working fluid to have two basic problems. The first is the possibility that the water working fluid will freeze when the units are shut down and the second is the need to vent any hydrogen gas that is generated within the heat exchanger due to the water working fluid reacting with the tube metallurgy.
With respect to the first problem, when an inclined heat exchanger is shut down, such as for repairs, fluid will collect in the lower portion (the hot or gas side) of the inclined heat pipes. Thus, if certain conditions occur, this fluid may freeze resulting in damage to the heat pipe tube due to the expansion of the fluid when it freezes.
With respect to the second problem, water working fluid often reacts with the tube metallurgy (generally carbon steel) to generate hydrogen gas. This hydrogen gas blankets off or insulates the interior surface of the heat tube from the working fluid thereby reducing any heat transfer that may occur. To alleviate this condition and to restore the efficiency of the heat exchange unit, the hydrogen gas must be vented, or "burped", from the tube on a somewhat regular basis.
In the past, when addressing the first problem, it was common to add an anti-freeze solution to the water working fluid in order to lower the freezing point of the fluid. Provided sufficient quantities of anti-freeze were added and this substance did not break down during use, it could be generally assumed that this problem was, at least temporarily, resolved. However, should the anti-freeze solution settle out or break down, such as by forming deposits in the heat tube, the efficiency and productivity of the heat exchanger would be impaired.
Regarding solutions to the second problem, various devices have been developed that are capable of venting hydrogen gas from the heat tube. Some such devices consist of typical pressure relief valves. Other solutions have included attempts to block the generation of hydrogen gas within the tube through chemical reaction, lining, or the like. However, unless these solutions are consistently monitored for proper operation, hydrogen gas may be generated which is not released soon thereafter. Additionally, to release such gas after it has been generated, it was first necessary to pressurize the system. Consequently, the method of achieving such pressurization must be continuously monitored to prevent any pressure build-up from occurring.
It is thus an object of this invention to provide a means of resolving both of the above identified problems without requiring special or elaborate equipment. Another object of this invention is to resolve both problems with the same piece of equipment thereby eliminating the need for separate or duplicate machinery. Yet another object of this invention is to provide a solution whose operation can be easily monitored and one which can be repaired quickly and easily, or replaced, should it become necessary to do so. Another object of this invention is to provide a solution that can be selectively activated such that it may be removed from service when not needed thereby reducing energy requirements. Still another object of this invention is to provide a solution that is operational for water working fluids in carbon steel heat tubes as well as for other types of working fluids in heat tubes of different metallurgy. These and other objects and advantages of this invention will become obvious upon further investigation.